Determination of flat-band voltages for fully depleted silicon-on-insulator (SOI) metal-oxide-semiconductor field-effect transistors (MOSFET's)

A method to determine the flat-band voltage, VFB, in silicon-on-insulator (SOI) metal-oxide semiconductor (MOS) structures has been proposed. It is based on the measurement of the back channel threshold voltages of SOI MOS field-effect transistors (MOSFET's) as a function of the front gate bias. This method is very useful for fully depleted SOI MOSFET's with a low channel dopant concentration. Mean values of VFB's obtained from this method were -0.79 V for n+ polysilicon gate SOI n-MOSFET's with a gate oxide of 205 Armstrong and an acceptor concentration of 4×1015 cm-3, and -0.12 V for n+ polysilicon gate SOI p-MOSFET's with a gate oxide of 205 Armstrong and a donor concentration of 5×1015 cm-3. The accuracy in the determination of VFB is mainly dependent on precise evaluations of the front gate oxide thickness, the surface silicon thickness, and the channel dopant concentration.